β-Ga2O3 crystals doped with the donor impurities Si or Sn are investigated by Raman spectroscopy. In addition to the well-known intrinsic Raman allowed phonon modes, we discover several spectral features when the doping concentration exceeds the Mott criterion for the metal-insulator transition (∼ 3 × 1018 cm−3). The most prominent extra Raman peak at 255 cm−1 is an asymmetrically broadened one. It is due to single-particle, electronic excitations involving the impurity band formed by effective-mass-like (hydrogenic) shallow donors. A similar type of excitation is attributed to a Raman line at 675 cm−1 that appears below room temperature in Si doped samples and might be due to a non-hydrogenic donor. Furthermore, we observe four longitudinal phonon-plasmon coupled modes at 215 cm−1, 280 cm−1, 400 cm−1, and 560 cm−1 associated with infrared active phonon modes. They arise from inelastic light scattering via charge-density fluctuations.

中文翻译：

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重施主掺杂 β-Ga2O3 中的拉曼散射

通过拉曼光谱研究了掺杂有施主杂质 Si 或 Sn 的 β-Ga2O3 晶体。除了众所周知的本征拉曼允许声子模式之外，当掺杂浓度超过金属-绝缘体转变的莫特标准（~ 3 × 1018 cm-3）时，我们发现了几个光谱特征。255 cm-1 处最突出的额外拉曼峰是一个不对称加宽的峰。这是由于单粒子电子激发涉及由有效质量（氢）浅供体形成的杂质带。类似类型的激发归因于 675 cm-1 处的拉曼线，该线出现在 Si 掺杂样品中低于室温，可能是由于非氢供体。此外，我们在 215 cm-1、280 cm-1、400 cm-1、和 560 cm-1 与红外有源声子模式相关。它们是由电荷密度波动引起的非弹性光散射引起的。